Different methods of image formation are known, such as thermal printing, ink jet printing, electrography, and electrophotography. These printing methods, particularly thermal printing and ink jet printing, are gaining in popularity. To form such prints, an electronic picture can be subjected to color separation by color filters. The respective color-separated images can be converted into electrical signals. These signals can be operated on to produce signals corresponding to respective colors, such as cyan, magenta, and yellow. These signals can be transmitted to a printer. To obtain a print, each color can be printed successively on the receiver.
To reduce costs associated with forming image-receiving elements for use in printing systems such as thermal printing, ink jet printing, electrography, and electrophotography, polymeric image-image-receiving elements can be formed at least in part by extrusion. One or more layers, such as the image-receiving layer, a tie (adhesive) layer, or both, can be extruded onto the support. Methods and materials suitable for extruded thermal receivers are disclosed, for example, in U.S. Pat. Nos. 6,939,828, 6,897,183, and 6,893,592 to Arrington et al., U.S. Patent Publications Nos. US 2004/0167020 to Arrington et al., and US 2004/0166343, US 2004/0175570, and 2004/0167021 to Kung et al., and pending U.S. application Ser. No. 11/035,329, filed Jan. 13, 2005, to Kung et al.
Polymers favored for use in extrusion coating include polyesters, polycarbonates, and combinations thereof due to their stability. To increase the thermal stability, stabilizers such as phosphorus-containing compositions have been added to polymeric compositions. Known phosphorous-containing stabilizers include a phosphorous acid, an organic diphosphite such as bis(2-ethylhexyl)phosphite, a phosphate, an alkyl phosphate, an aryl phosphate, an inorganic phosphate, a phosphoric acid ester, or a phosphorous acid. The phosphorous-containing stabilizer can be combined with a plasticizer such as dioctyl sebacate before addition to the polymeric composition. However, even with stabilizers, the composition may only be stable for a few minutes, requiring extrusion to proceed at a rapid pace and/or use of small quantities of material. If not all material is extruded within a short period of time, for example, less than fifteen minutes, the composition can exhibit unacceptably high levels of cross-linking, resulting in a higher viscosity and uneven polymeric flow, causing voids or streaks in the cast sheet, or the composition can exhibit an unacceptable level of thermal degradation, resulting in streaks or a more liquid composition that does not properly set.
There is a need in the art for a means to reduce the amounts of additives in an image-receiving element, and maintain good print image formation, while still reducing or eliminating donor-receiver sticking. There is also a need to provide an image-receiving element capable of formation by extrusion coating to reduce costs. There is an additional need for stabilization, for example, at extrusion temperatures, in oxidative conditions, or both, to enable longer extrusion times and use of larger amounts of extrudate.